<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>转化div#demo.demo</title>
</head>
<body>
    <script>
        const reg = /\S+#\S+\.\S+/
        const r = 'div#demo.demo'.replace(reg,'<div id="demo" class="demo"></div>')
        console.log(r)
    </script>
</body>
</html>